Series arc welder

ABSTRACT

An electric arc welder for depositing weld metal along a groove between two edges of a metal workpiece. The welder comprises: a leading electrode driven toward a point in the groove by a first wire feeder operated at a first speed by a first motor with a speed control input and a tachometer derived first feedback signal, a trailing electrode driven toward the same point by a second wire feeder operated at a second speed by a second motor with a speed control input and a tachometer derived second feedback signal, a first power source directing a first current to flow through the leading electrode and a second power source causing a second current to flow through the trailing electrode with the current flow being in a series arc circuit. The second power source being grounded to the workpiece to modify the series arc current so ground current flows to the workpiece whereby the second current is generally equal to the first current minus the ground current.

The present invention relates to the art of electric arc welding andmore particularly to an improved series arc welder as disclosed in Shutt4,246,463.

INCORPORATION BY REFERENCE

For over twenty years, submerged arc welding has often been performed bya series arc process wherein two welding wires are fed to anintersecting point above the workpiece with an electric arc between thetwo advancing welding wires. The wires or electrodes are melted todeposit metal into the groove between two spaced metal plates to bejoined. These may be a seam in a pipe or pipeline. In the mid-1970's,this well known submerged arc welding process was modified to create notonly an arc between the two intersecting electrodes, but also an arcbetween the electrode and the workpiece to stabilize the melting arc.This improvement is called the modified series arc welding process andis described in Shutt 4,246,463, incorporated by reference herein. Thisprior patent also describes in detail the prior series arc weldingprocess. These two procedures are used primarily in submerged arcwelding as the leading process to join the gap between the spaced platespreparatory to a subsequent tandem welding operation by one or morefollowing electrodes. Background to the present invention is the seriesarc welder and the modified series arc welder as described and shown inShutt 4,246,463.

THE INVENTION

In accordance with the first aspect of the invention, there is providedan electric welder for depositing weld metal along a groove between twoedges of a metal workpiece. The welder comprises a leading electrodedriven toward a point in the groove by a first wire feeder operated at aspeed by a first motor having a speed control input. A trailingelectrode is driven toward the same point by a second wire feederoperated at a second speed by a second independent motor with a speedcontrol input. A power source creates an arc between the electrodes tomelt the electrodes and fill the groove. The first motor for the firstwire feeder has a tachometer to generate a feedback WFS signal. Thissignal is the feedback signal to the single power source including awire feed speed controlling device or program for creating a control WFSsignal. The control input of the first motor receives the WFS signal sothis first wire feeder is driven at a set speed based on the feedsignal. The power source generates only one WFS signal to control thewire feed speed of the first wire feeder. The second wire feeder isdriven by a slave circuit connected to the WFS signal for controllingthe the second wire feeder.

In the past, a series arc welder has two wire feeders with a single WFSsignal for both wire feeders. Thus, neither wire feeder operated atoptimum feed speed. By using the present invention, a single powersource creates a single WFS signal for both wire feeders; however, thissingle signal is controlled by a feedback loop from one of the firstwire feeders so that the speed of at least one wire feeder is optimized.The other electrode of the welder is driven by a slave circuit. Usingthe invention for a series arc welder, a single power source creates acontrolled wire feed speed for one of the motors and the other motor isdriven by a slave circuit. In accordance with another version of thepresent invention, the slave circuit includes a device for decreasingthe level of the feedback control WFS signal used for control of thefirst wire feeder. This reduced level signal is then the control inputof the motor for the second wire feeder. In this manner, the feedbackcontrolled signal from the single power source drives one wire feeder ata controlled speed and the other wire feeder by a reduced signalcreating a lower speed. If the feedback controlled first wire feeder isto operate at a speed less than the slave circuit driven wire feeder, adevice is used to reduce the level of the control signal from the powersource before it is directed to the first wire feeder. Consequently, inaccordance with the present invention, the power source creates afeedback signal for controlling one wire feeder. The same signaloperates through a slave circuit to control the other wire feeder. Toadjust the relative speed between the two motors, either the mastercircuit or the slave circuit can be provided with a device such as aresistor to decrease the level of input control for each of the two wirefeeders. Different speeds can also be obtained by using the singlefeedback WFS signal with different ratio gear reducers in the twomotors. In this manner, the first motor is controlled by its feedbackWFS signal, but a slave circuit controls the other motor to operate at adifferent speed, even though the magnitude of the actual control signalfrom the power source is the same.

The invention can be used in both a series arc welder and a modifiedseries arc welder where a single motor creates a single output signal.In the past, one signal controlled two separate wire feeders, unlesscomplicated internal programming was provided in the wire feeder. Thepresent invention uses a master feedback control for one of the wirefeeders and a novel slave control concept for controlling the speed ofthe other wire feeder.

In accordance with another aspect of the present invention, the seriesarc welder is driven by two separate power sources connected to theleading and trailing electrodes. Current in the leading electrode isdirected through the trailing electrode in accordance with a series arcconfiguration. Since there are two separate power sources, each of themotors for the wire feeder has a tachometer to create a feedback signalwhereby each of the wire feeders is controlled to the desired wire feedspeed. The desired wire feed speed is adjusted by an arc voltagefeedback so the feed speed is controlled by the arc length. Using thisconcept, a selected voltage associated with the first electrode and aselected voltage associated with the second electrode are used to adjustthe desired wire feed speeds of the separate wire feeders. The feedbackvoltage adjusts the desired wire feed speed and is compared with thefeedback signal from the tachometer. Thus, using two power sources, eachof the wire feeders is controlled with feedback from the drive motor ofthe feeder. To adjust the desired speed the voltage associated with thetwo electrodes is used. Two power sources constitute a novelconfiguration for a series welder. It also is novel for a modifiedseries welder.

In accordance with an aspect of the invention, the single power sourcein the first embodiment and the two power sources in the secondembodiment use a connection to the workpiece. This creates a modifiedseries welder and transfers the arc from between the two electrodes onlyto an arc that is also between the two electrodes and workpiece. In thismodified series procedure, the inventive control of the wire feeders aspreviously described prevents instability when there is a short betweenthe electrode and the workpiece. When there is a short, the groundcurrent from the electrodes to the workpiece increases substantially.Since the current on the trailing electrode is the difference betweenthe current on the leading electrode and the ground current, the secondor trailing electrode has drastically reduced current. A typical powersource is programmed to increase or ramp up its output current whenthere is a short circuit to clear the short. When the standard shortclearance routine is executed by a detected short the increased currentfrom the power source attempts to control the current in the groundconnection and actually reduce the current in the short circuit. This isan unstable situation that is associated with a short in either theseries arc welder or the modified series arc welder. In accordance withanother aspect of the invention, a short circuit is detected. At thattime, a program is used to clear the short by controlling the current ofthe second power source. The program can perform in various routines.For instance, a routine can decrease the current in the second powersource or can maintain the current in the second power sourcesubstantially constant. The second power source is a constant currentpower source to execute these programmed routines.

In accordance with an aspect of the invention, when two power sourcesare used, they can be connected in either series or in parallel.Furthermore, they can be connected in a series arc or modified seriesarc configuration.

The primary object of the present invention is the provision of animproved series arc welder. Yet another object of the invention is theprovision of a welder as defined above, which welder uses a single powersource accurately controlling the wire feed speed of the leadingelectrode. Another object of the present invention is the provision of awelder using two power sources with feedback control of both wirefeeders.

Still a further object of the invention is the provision of welders asdefined above, which welders are connected in modified series whereincurrent is provided to the workpiece for creating a controlled arcbetween the intersecting electrodes.

Still a further object of the present invention is the provision of amodified series arc welder having improved control of the wire speedduring operation of the welder and having a circuit for controlling thecurrent in the power source when there is a short circuit.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a wiring diagram of the first embodiment of the presentinvention;

FIG. 2 is an enlarged cross-sectional view taken generally along line2-2 of FIG. 1;

FIG. 3 is a block diagram of the Power Wave power source used in thesingle power source of the first embodiment shown in FIG. 1 and alsoused for both power sources of the second embodiment shown in FIG. 11;FIG. 4 is a schematic wiring diagram illustrating the inventiveimprovement in the embodiment of the invention;

FIGS. 5, 6 and 7 are simplified wiring diagrams of a different versionof the inventive improvement shown in FIG. 4;

FIG. 8 is a side elevational view of a submerged arc welding processusing a welder with two power sources and operated in the series arcconfiguration;

FIG. 9 is a side elevational view similar to FIG. 8 wherein the welderperforms a modified series arc process;

FIG. 10 is the AC waveform used for the three power sources shown inFIGS. 8 and 9;

FIG. 11 is a wiring diagram of the second embodiment of the presentinvention utilizing two power sources for a modified series arc weldingprocess;

FIG. 11A is a block diagram of the circuits to adjust the desired wirefeed speeds in the welder shown in FIG. 11;

FIGS. 12 and 13 are block diagrams of the circuits used by bothembodiments of the invention for responding to a short circuit; and,

FIG. 14 is a diagram illustrating a modification of the secondembodiment of the present invention as shown in FIG. 11 wherein the twopower sources are connected in parallel and used for modified serieswelding.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiment of the invention and not tolimit same, FIGS. 1 and 2 show an arc welder A using a modified seriesconcept as described in Shutt 4,246,463 incorporated by referenceherein. The invention involves an electric arc welder schematicallyillustrated as a submerged arc process. The weld performs tandemelectric arc welding where first electrode E1 and second electrode E2are connected in modified series. Subsequent electrodes, one of which isillustrated as electrode E3, travel in unison with electrodes E1 and E2and perform a tandem sub arc welding process. Of course, more than onetrailing electrode E3 is normally used. The technology described inShutt 4,246,463 is applicable to electric arc welder A used to depositmetal in groove 10 of workpiece WP. In the illustrated embodiment,workpiece WP is spaced plates 12, 14 with a small gap b where edges 20,22 define trough or groove 24 having an angle 26, best shown in FIG. 2.Electrodes E1, E2 are directed toward a point in groove 24, best shownin FIG. 2. This point is below the electrical contact sleeve or tip 70,and defines a stickout h. Referring now more specifically to FIG. 1,mechanism 40 contains electrodes E1, E2 and drives them along groove 10and includes a main power source 42, with output terminals 44, 46 todirect AC current by way of leads 50, 52 to the respective electrodesE1, E2. These electrodes are welding wires supplied from spool 60, 62,respectively, and driven through contacts tips 70, 72 by standard wirefeeders 80, 82, respectively. Wire feeder 80 includes drive rolls 80 a,80 b rotated by a motor 80 c. In a like manner, wire feeder 82 includesdrive rolls 82 a, 82 b rotated by motor 82 c. Leads 80 d and 82 d areboth powered by a control signal in line 84 from main power source 42.The power source is a Power Wave unit manufactured by The LincolnElectric Company of Cleveland, Ohio and is generally the state tableoperated welder disclosed in Blankenship 5,278,390. Power source 42 isused to control both wire feeders 80, 82. This results in a limitation,since only a single signal is available from the power source to drivethe wire feeder. Consequently, the signal on line 84 must be acompromise signal between the desired wire feed speed of electrodes E1,E2. In practice, the single signal on line 84 drives both wire feeders.This is an open loop control based upon the desired wire feed speedloaded into the controller of power source 42. However, as explainedlater, separate signals for the wire feeder are created when using twopower sources, as shown in FIG. 11.

Lead 52 is connected to contact tip 72 by line 90 and is connected toworkpiece WP by line 92. Thus, current flow between electrode E1 andpower source 42 is through a low resistance line 90 and a higherresistance line 92. The resistance of these return paths divides thecurrent flow to adjust the heat in the arc and control penetration bythe arc force in the welding process, as described in Shutt 4,246,463.By using the two electrode mechanism 40, high metal deposition isobtained by using series connected electrodes E1, E2 while actuallyusing low heat. A limited amount of current flows from electrode E1 intothe workpiece during the welding operation. This welding process of eachpower source is controllable in accordance with the preferred embodimentof the present invention, by the program and architecture schematicallyillustrated in FIG. 3.

In accordance with the practical embodiment of the invention, electrodesE1 and E2 are trailed by at least one electrode E3, shown in FIG. 2.This trailing electrode is moved by single electrode mechanism 100 inunison with two electrode mechanism 40 moving electrodes E1, E2. The twomechanisms may be integrated or separately operated. In the preferredembodiment, the same moving device is used for mechanisms 40, 100. Thetrailing electrode mechanism includes auxiliary power source 102 whichis also a Power Wave unit manufactured by The Lincoln Electric Companyof Cleveland, Ohio and operated by the technique shown in FIG. 3. Powersource 102 has output terminals 104, 106 for directing an AC currentwaveform by way of lines 110, 112 to employ electrode E3 in a submergedarc welding process. Electrode E3 is a wire supplied by spool 114 and isdriven through contact tip 120 by wire feeder 130. This feature issimilar to wire feeders 80, 82 of electrodes E1, E2. Wire feeder 130 hasspaced drive rolls 130 a, 130 b rotated by a motor 130 c. A controlsignal from power source 102 in line 132 drives motor 130 c to feedelectrode E3 toward workpiece WP at a speed determined by the signal inline 132.

In operation of the embodiment illustrated in FIGS. 1 and 2, electrodesE1, E2 and trailing electrode E3 create a weld puddle 150 in groove 10.Electrodes E1, E2 create a first root pass that joins or tacks edges 20,22 together by melting the inwardly projecting portions of groove 10.Granular flux 152 is deposited in front of electrode E1. Thereafter,puddle 150 is formed to displace flux 152 and is covered by bead 154deposited by electrode E3. In practice, all electrodes are used in asubmerged arc welding process. Flux dispenser 160 is moved in front ofelectrode E3 and has a dispensing motor 162 for dispensing flux F fromhopper 164 through tube 166 in accordance with standard submergedwelding technology. A similar flux dispenser 160 is then provided abovegroove 10 in front of electrode E1 to deposit flux 152. In practice, ashielding gas is employed around electrodes E1, E2. The presentinvention utilizes a Power Wave power source for the main power source42 and for the auxiliary power source 102 having output terminals104,106. These power sources are operated by a digital controller anduse a waveform technology process pioneered by The Lincoln ElectricCompany where the power sources create waveforms defined by a statetable. A series of individual current pulses created at a high switchingspeed in excess of 18 kHz cause a selected waveform to be outputted fromthe power source. In practice, the waveforms are provided by a series ofcurrent pulses created at a rate of over 40 kHz. In this manner, bothleading mechanism 40 and following mechanism 100 include a power sourcethat outputs a desired AC waveform to optimize the welding process forthe two series electrodes E1, E2, as well as the trailing electrode E3.Such power source operation is schematically illustrated in FIG. 3,which represents the type of power sources used in practicing thepreferred embodiments of the present invention and shown in FIGS. 1 and11.

System 200 of the present invention is schematically illustrated in FIG.3 wherein a Power Wave power source 210 has an input supply 214 and ahigh switching output stage 212 with output terminals 212 a and 212 b.Output stage 212 creates an AC waveform at output terminals 212 a, 212 bto perform an AC arc welding process at the weld station illustrated asincluding electrode 220 and workpiece 222 and having a current shunt 230to output a signal in line 232. This signal represents the current ofthe welding process being performed. Comparator 240 receives the signalon line 232 and has an output 240 a with a voltage controlling pulsewidth modulator circuit 242, which can be digital or analog and has avariety of configurations. The pulse width modulator is driven at highspeed by oscillator 244 which, in practice, operates at a frequency ofabout 40 kHz. This frequency of the oscillator drives the pulse widthmodulator and provides a series of current pulses at a high speedswitching rate to create an AC waveform at the weld station. Thepolarity of the waveform is controlled by the logic or signal fromnetwork 250 having an input line 252 from waveform generator 260 and anoutput line 254 for controlling the polarity of the waveform outputtedfrom stage 212 of the Power Wave power source unit. The profile of thewaveform comprising a series of rapidly created pulses is controlled anddictated by waveform generator 260 having a select network 262 whichselects the desired waveform to be created at output terminals 212 a,212 b of stage 212. By the selected waveform from network 262, thedesired waveform is created for use by the electric arc weldingmechanisms 40 and 100. To control the waveform used for the seriesconnected electrodes E1, E2, system 200 includes waveform adjustingcircuits 272-278, each having adjusting networks 272 a-278 a. Circuit272 adjusts the frequency of the waveform. After the waveform isselected by network 262, a signal from circuit 272 adjusts the frequencyof the AC waveform. In a like manner, the duty cycle of the waveform iscontrolled by circuit 272. Duty cycle is the time the waveform is in thepositive polarity compared to the time in the negative polarity.Circuits 276 and 278 control the magnitude of the current during thenegative portion of the waveform or the positive portion of thewaveform. Circuit 276 is to adjust the magnitude of the negative portionof the waveform. Circuit 278 adjusts the magnitude of the positiveportion of the waveform. The waveform used for electrodes E1, E2 is anAC waveform. However, a DC waveform could be used for a trailingelectrode E3, although AC current is preferred. Indeed, it is preferredto use an AC waveform for all electrodes of electric arc welder A asshown in FIG. 10. Other circuits have been used to adjust the signal online 270 to modulate and change the profile of the wave shape selectedby network 262 to optimize welding at the intersection of electrodes E1,E2.

A two power source modification of the preferred embodiment illustratedin FIGS. 1-3 is schematically illustrated in FIG. 11 which shows tandemelectrode welder 290 including a main power source 292 and a secondpower source 294. The main power source 292 has output terminals 296 aand 296 b. These terminals are connected to leads 292 a and 292 b,respectively. Lead 292 a connects the one output of power source 292 tocontact tip 70 of electrode E1. Lead 292 b is connected to line 300 forcurrent flow in a path to and from electrode E2. To connect terminal 296b in the path of the workpiece ground, second power source 294 isconnected in series between terminal 296 b and workpiece WP using lead294 b. Second power source 294 has terminals 298 a connected to lead 294a and terminal 298 b connected to lead 294 b. In this manner, secondpower source 294 is in series with the lead 294 b connected to terminal298 b and lead 302. In this architecture, electrode E1 carries fullcurrent and the current to and from electrode E1 is divided betweenelectrode E2 and the circuit including leads 294 b and 302. Lead 294 afrom terminal 298 a is connected to lead 292 b from power source 292.Consequently, the two power sources 292 and 294 are connected in seriesbetween the ground lead 294 b and lead 292 a. Between the two powersources, line 300 is connected to contact tip 72 of electrode E2.Consequently, electrodes E1 and E2 are in series with a ground currentpath through Power Wave power source 294. By using this arrangement, thewaveforms used for both power source 292 and 294 are the same and areeach created by a system 200 as shown in FIG. 3. Adjustments are made tothe waveform process by power source 294 to control the current flowingin the ground path of the welder. Control of power source 294 isaccomplished by regulating the current in lead or line 302 flowing toand from workpiece WP. Since two separate power sources are employed,wire feeder 80 is controlled by the signal on line 292 c from powersource 292. A second wire feeder signal in line 294 c is controlled bypower source 294. Welder 290 has the advantage of being able to controlwire feeders 80, 82 separately without complex software in the powersource digital control section. A main power source could have twoparallel modules as illustrated in FIG. 14, but FIG. 11 uses seriesconnected modules or power sources. The second power source is connectedin series with the ground lead 302 to better control the currentwaveform in the ground return circuit or path.

The various technology concepts in Shutt 4,246,463 are applicable to theseries arc connected welder shown in FIGS. 1-3 and shown in FIG. 11.These welders have two front electrodes connected in series and have acurrent return path through the workpiece. The front welders arecombined with trailing welders to perform a tandem submerged arc weld.

In accordance with the invention, when using a single power source asshown in FIGS. 1 and 2, the wire feeders are controlled by a singlesection 310 in the digital controller of power source 42. Controllersection 310 receives a wire feed speed signal on line 312 and convertsthe DC voltage on terminals 314, 316 into a DC output signal fromvoltage signal generator 320 on output lines 322, 324. In accordancewith normal practice the signal on line 312 is often adjusted tomaintain a given arc length. In accordance with the wire feed speedcontrol mechanism of FIG. 4 as using a single power source embodiment,the same DC voltage on lines 322, 324 is supplied to both motor 80 c andmotor 82 c to drive electrode E1 and electrode E2 in unison toward theintersecting point, where a series arc is created to melt the electrodesand fill the gap in groove 10 of workpiece WP. In accordance with thisarrangement, motor 80 c has an output tachometer 330 creating a voltageon line 332. This voltage represents the speed of motor M1 drivingleading electrode or wire E1 toward workpiece WP. First motor M1 iscontrolled by a feedback loop including error amplifier 334 generatingan output error signal in line 336 determined by the relationship of theactual feed speed represented by the voltage on line 332 and the set oradjusted desired feed speed as represented by the voltage or digitalsignal on line 312. Consequently, motor M1 has a tachometer thatgenerates a feedback WFS signal so the section 310 creates a control WFSsignal across output lines 322, 324. First motor M1 is maintained at theset or adjusted wire feed speed represented by the voltage or digitalsignal on line 312. A slave circuit 340 is preferably formed as leads342, 344 to drive motor 82 c. In this implementation of the presentinvention, motor M1 and motor M2 are driven in unison by the same ACvoltage. Slave circuit 340 is merely an extension of output lines 322,324, so the voltage on both motor M1 and motor M2 are the same. Thus,the two motors are driven at the same speed and the lead motor M1 isregulated by a feedback loop. In this manner, one of the wire feeders isdriven at optimum, desired speed. This speed is controlled. The othermotor merely follows at a related speed. This novel feature is modifiedslightly as shown in FIGS. 5-7. In FIG. 5, the slave circuit is rheostat340 a so that the voltage on leads 342, 344 is adjusted to a lower levelthan the voltage on lines 322, 324. Consequently, motor M2 is adjustedto operate at a slightly slower speed than motor M1. In a like manner,motor M1 can be adjusted by rheostat 360 to operate at slightly lowerspeed than motor M2, as illustrated in the version shown in FIG. 6.Rheostat 360 is connected between lines 322, 324 and motor M1. Slavecircuit 340 is the same as used in the version shown in FIG. 4. By usingthis version of the invention, motor M1 is driven at a fixed feedbackcontrol speed but the motor M2 is driven at a higher speed. By using thetechniques or versions shown in FIGS. 5 and 6, the second motor is stilldriven as a slave; however, this slave driven motor can be operated at aspeed below or a speed above the feedback speed of motor M1. A furtherversion of this concept is illustrated in FIG. 7 wherein the slavecircuit is boost converter 370 having an output controlled by rheostat372. The voltage on leads 342, 344 is greater than the voltage on lines322, 324. Motor M2 is driven at a speed higher than motor M1. Of course,a buck converter could be used for the slave circuit so that the voltagedriving motor M2 is less than the voltage driving motor M1. In allinstances, leading electrode E1 has a feedback loop controlled wire feedspeed and trailing electrode E2 is driven at a speed in a fixedrelationship to the speed of motor M1. One of the motors is optimized,while the other motor has a correlated wire feed speed. In accordancewith another aspect of the invention, each of the motors M1, M2 couldhave a gear reducer with a different gear ratio. These concepts form anaspect of the invention wherein one of the wire feeders in a singlepower source version of the present invention is controlled by astandard feedback circuit whereas the second wire feeder is correlatedwith the first wire feeder in a master-slave arrangement.

As so far described, the invention is a version used with a single powersource welder as shown in FIGS. 1-4. The second embodiment of thepresent invention is illustrated in FIG. 11 wherein a single powersource is replaced by two power sources 292, 294 connected in series andalready generally described. The concept of FIG. 4 used for the singlepower source welder is also applicable to the two power source welder ofFIG. 11. The welder in FIG. 11 is provided with a first wire feeder 400for driving electrode or wire E1 toward workpiece WP by motor M1. Thefirst motor is controlled by signals through lead 292 c connected tofirst power source 292 and shown as a coaxial cable. One of thesesignals is a voltage on line 402, which is a DC signal actually usingtwo lines for directing a DC voltage signal to motor M1. Motor M1 hastachometer 406 to generate a voltage on line 404 which is the feedbacksignal used to control the wire feed speed and, thus, the DC voltagesignal on line 402. In a like manner, second wire feeder 410 is drivenby motor M2 through lead 294 c which is actually a coaxial cableconnected to the controller of second power source 294. Coaxial line orcable 294 c includes a line 412 having a DC voltage for driving motor M2at a speed determined by the level of the DC voltage. Tachometer 416creates a voltage in line 414 forming the feedback signal to control thewire feed speed of feeder 410. Thus, power source 292 controls motor M1of feeder 410 with a feedback loop. A feedback loop or circuit is alsoused to control the speed of feeder 410. Two power sources are used forthe series arc welding by electrodes E1, E2. Each of the wire feeders isseparately controlled by one of two power sources 292, 294. To adjustthe desired wire feed speed controlled by the signal on line 404, it isnecessary to sense a relevant voltage at a selected location in thewelding associated with electrode E1. In the preferred implementation, avoltage is sensed by circuit or device 420 connected to the workpiecelead 302 by line 422 and to contact tip 70 by line 424. Circuit ordevice 420 provides a voltage on line 420 a which adjusts the desiredwire feed speed to be controlled by the signals through lead 292 c.Other voltage associated with electrode E1 can be used to control thewire feed speed of feeder 400. Option circuit or device 440 has anoutput voltage on line 430 a controlled by voltage between contact tips70, 72 using lines 432, 434. To adjust the wire feed speed of secondmotor M2 voltage, voltage sensing circuit or device 450 has an output450 a with a voltage signal indicative of the voltage between contacttip 72 as read by line 452 and workpiece WP as read by line 454 fromlead 302 through line 422. The signal on output line 450 a adjusts thewire feed speed of feeder 410 and the signal on line 420 a adjusts thewire feed speed of feeder 400. By using two separate power sources, thewire feeders 400, 410 can be separately adjusted to optimize theoperation of the series welder shown in FIG. 11. Power sources 292, 294are connected in series and are moved in unison along workpiece WP. Thewelding operation is a modified series arc process, even though theinvention could be used in a series arc welding process.

The technical distinction between series arc and modified series arcusing the novel concept of two power sources as shown in FIG. 11 isschematically represented in FIGS. 8 and 9. In FIG. 8, the powersupplies 292, 294 are connected in series across electrodes E1, E2. Thisconnection creates a series arc SA to melt electrodes E1, E2 for formingmolten metal bead B1. Trailing electrode E3 receives a waveform frompower source 102 to form a subsequent molten metal bead B2. The weldershown in FIG. 11 can be used for series arc welding as schematicallyillustrated in FIG. 8. By connecting terminal 298 b between power source294 and workpiece WP by line 300, a modified series arc welding processis implemented, as shown in FIG. 9. Modified series arc MSA is createdbetween electrode E1 and electrode E2 and is also directed to workpieceWP, as described in Shutt 4,246,463. Thus, the welder shown in FIG. 11can be connected in a series arc configuration of FIG. 8 or the modifiedseries arc configuration of FIG. 9.

Since the second embodiment of the invention as shown in FIG. 11involves using two separate power sources, waveform generator 260associated with each power source creates a waveform 500 so that thesame waveform is outputted from the two power sources. Waveform 500 forboth power sources is created in unison, as shown in FIG. 10; however,the actual current is 180° out of phase in electrodes E1, E2. The powersource for tandem electrode E3 is AC waveform 502 which is out of phasewith waveform 500 of the two power sources. The phase shift ispreferably 90° as shown in FIG. 10. In summary, the waveforms from thefirst and second power sources are AC waveforms in phase and thewaveform for tandem electrode E3 is an AC waveform which is out ofphase. The concepts schematically illustrated in FIGS. 8, 9 and 10 arepresented to explain the operation and certain features of theembodiment of the invention shown in FIG. 11.

To create the wire feed speed for feeder 400 and feeder 410, the digitalcircuits of the power sources used in the welder shown in FIG. 11utilizes the voltages on lines 420 a and 450 a, as schematicallyillustrated in FIG. 11A. The digital circuits are shown in analogcomponents. The instantaneous voltage from voltage circuit or device 420on lines 420 a is averaged by digital circuit 510 to produce average V1voltage on line 512. This average voltage is compared with a set voltageon line 514 by error amplifier 516 to create an error signal on line518. This signal is used to adjust the wire feed speed of feeder 400. Ina like manner, the voltage signal on output line 450 a is averaged bycircuit 520 to produce an average V2 voltage signal on line 522. Thissignal is compared to the set voltage on line 524 by error amplifier 526to produce an error signal on line 528. This signal adjusts the wirefeed speed of feeder 410. The signals on line 518 and 528 are used tocontrol the speed of motors M1, M2. FIGS. 11 and 11A illustrate theseparate control of the two wire feed speeds when using two separatepower sources for the series arc welder of FIG. 8 or modified series arcwelder of FIG. 9.

As indicated in FIG. 11, the current from the electrodes to theworkpiece is ground current I_(G). Most inverter type power sources havea standard program for clearing a short between the electrode andworkpiece. When there is a short circuit, the ground currentI_(g)increases drastically. To clear the short, the current of the powersource is ramped up to burn away the short circuit. When doing this inan architecture involving a modified series arc, as the ground currentincreases, the current on electrode E2 drastically decreases since powersource 294 regulates current in lead 302. This reaction to a shortreduces the melting of the second electrode and has a tendency to causethe electrode to be projected against the workpiece. As the current ofpower source 294 increases, current I_(g)in the arc decreases. This hascreated instability. In accordance with an aspect of the invention, thissituation involved in a modified series arc welder is rectified orreduced in importance by a circuit which detects the short and thencontrols the current in electrode E2 with a program that actuallycontrols the current of power source 294 for the purpose of maintainingmelting of electrode E2. Furthermore, when electrode E2 is grounded, V2decreases drastically which affects the wire feed speed control setforth in FIG. 11A. To rectify this current deficiency and correct thespeed of the electrode advancing toward the workpiece, a program isemployed such as shown in FIG. 12 wherein the voltage across contact ortip 72 and workpiece WP is directed to a standard short detect circuit600. When there is a short, V2 is reduced and a logic appears on line602 to activate digital control program 604, which program is a routinethat attempts to maintain the current in power source 294 at a givenlevel to effect clearing of the short circuit and decrease the wire feedspeed of feeder 410. However, an alternate technique is illustrated inFIG. 13 wherein short detector circuit 610 produces a short signal online 612 to activate digital program 614. This program decreases currentof power source 294. This creates the tendency to decrease the groundcurrent and increase the current in electrode E2. The two circuits shownin FIGS. 12 and 13 are representative in nature and are used to performan aspect of the invention, wherein a short circuit is detected soconstant current power source 294 is controlled to burn away the shortcircuit and control movement of electrode E2 toward the workpiece. Otherprograms can be used to control the actual current in electrode E2 orthe current created by the second power source.

The invention involves the use of two power sources for use in amodified series arc welding process. In the preferred embodiment of theinvention, the two power sources are connected in series, as shown inFIG. 11; however, they may be connected in parallel as schematicallyillustrated in FIG. 14. Terminal 296 a of power source 292 is connectedto terminal 298 a of power source 294. In like manner, terminal 296 b isconnected to terminal 298 b. To drive contact tip 72, terminal 298 b isconnected by low resistance lead 620 and the workpiece is connected bylead 622. To show the versatility of the present invention, the wirefeed speed of feeder 400 is controlled by a WFS signal on line 294 cfrom second power source 294. The first power source 292 controls thespeed of feeder 410 by a signal on line 292 c. Both of these signals arecreated by a feedback technique already described. The various voltagesfor feedback control of the wire feed speed are within the skill of theart and need not be shown.

1. An electric arc welder for depositing weld metal along a groovebetween two edges or a metal workpiece, said welder comprising: aleading electrode driven toward a point in said groove by a first wirefeeder operated at a first speed by a first motor with a speed controlinput, a trailing electrode driven toward said point by a second wirefeeder operated at second speed by a second motor with a speed controlinput and a power source for creating an arc between said electrodes tomelt said electrodes, said first motor having a tachometer to generate afeedback WFS signal, said power source having a wire feed speedcontrolling device for creating a control WFS signal directed to thecontrol input of one of said motors to maintain said one motor at a setspeed based upon said feedback WFS signal and a slave circuit to connectsaid control WFS signal to the control input of the other of said motor.2. A welder as defined in claim 1 wherein said first and second speedare generally the same with said control WFS connected directly to bothsaid control input of said first motor and said control input of saidsecond motor.
 3. A welder as defined in claim 2 wherein one of saidtrailing electrode is grounded to said workpiece.
 4. A welder as definedin claim 1 wherein one of said electrodes is grounded to said workpiece.5. A welder as defined in claim 4 including a short detector to detect ashort between said trailing electrode and said workpiece and a circuitto maintain the current in said second electrode generally constantduring at least a portion of said short.
 6. A welder as defined in claim5 wherein said constant current is maintained during most of said short.7. A welder as defined in claim 4 including a short detector to detect ashort between said trailing electrode and said workpiece and a circuitto increase the current in the second electrode during at least aportion of said short.
 8. A welder as defined in claim 7 wherein saidincreased current is maintained during most of said short.
 9. A welderas defined in claim 1 including a short detector to detect a shortbetween said trailing electrode and said workpiece and a program tomaintain the current in said power source generally constant during atleast a portion of said short.
 10. A welder as defined in claim 9wherein said constant current is maintained during most of said short.11. A welder as defined in claim 1 including a short detector to detecta short between said trailing electrode and said workpiece and a programto decrease the current of said power source during at least a portionof said short.
 12. A welder as defined in claim 11 wherein saiddecreased current is maintained during most of said short.
 13. A welderas defined in claim 1 wherein said slave circuit includes a device fordecreasing the level of said control WFS signal before it is connectedto said control input of said second motor.
 14. A welder as defined inclaim 13 wherein said device is a buck converter.
 15. A welder asdefined in claim 1 including a device for reducing the level of saidcontrol WFS signal before it is connected to said control input of saidfirst motor.
 16. A welder as defined in claim 1 wherein said motors havedifferent ratio gear reducers to drive said wire feeders at differentspeeds.
 17. A welder as defined in claim 1 wherein said one of saidmotors is said first motor.
 18. An electric arc welder for depositingweld metal along a groove between two edges of a metal workpiece, saidwelder comprising: a leading electrode driven toward a point in saidgroove by a first wire feeder operated at a first speed by a first motorwith a speed control input and a tachometer derived first feedbacksignal, a trailing electrode driven toward said point by a second wirefeeder operated at a second speed by a second motor with a speed controlinput and a tachometer derived second feedback signal, a first powersource directing a first current to flow through said leading electrodeand a second power source causing a second current to flow through saidtrailing electrode with said current flow being in a series arc circuit.19. A welder as defined in claim 18 wherein said second power source isgrounded to said workpiece to modify said series arc current so groundcurrent flows to said workpiece whereby said second current is generallyequal to said first current minus said ground current.
 20. A welder asdefined in claim 19 wherein said first speed is generally equal to saidsecond speed.
 21. A welder as defined in claim 18 wherein said firstspeed is generally equal to said second speed.
 22. A welder as definedin claim 21 including a short detector to detect a short between saidtrailing electrode and said workpiece and a program to maintain thecurrent in said second power source generally constant during at least aportion of said short.
 23. A welder as defined in claim 22 wherein saidconstant current is maintained during most of said short.
 24. A welderas defined in claim 19 including a short detector to detect a shortbetween said trailing electrode and said workpiece and a program tomaintain the current in said second power source generally constantduring at least a portion of said short.
 25. A welder as defined inclaim 24 wherein said constant current is maintained during most of saidshort.
 26. A welder as defined in claim 18 including a short detector todetect a short between said trailing electrode and said workpiece and aprogram to maintain the current in said second power source generallyconstant during at least a portion of said short.
 27. A welder asdefined in claim 26 wherein said constant current is maintained duringmost of said short.
 28. A welder as defined in claim 21 including ashort detector to detect a short between said trailing electrode andsaid workpiece and a program to decrease the current of the second powersource during at least a portion of said short.
 29. A welder as definedin claim 28 wherein said decreased current is maintained during most ofsaid short.
 30. A welder as defined in claim 19 including a shortdetector to detect a short between said trailing electrode and saidworkpiece and a program to decrease the current in the second powersource during at least a portion of said short.
 31. A welder as definedin claim 30 wherein said decreased current is maintained during most ofsaid short.
 32. A welder as defined in claim 18 including a shortdetector to detect a short between said trailing electrode and saidworkpiece and a program to decrease the current in the second powersource during at least a portion of said short.
 33. A welder as definedin claim 32 wherein said decreased current is maintained during most ofsaid short.
 34. A welder as defined in claim 19 wherein each of saidpower sources includes a high speed switching output stage for creatingone of said currents with selected output waveform generated by awaveform generator controlling a pulse width modulator circuit todetermine the current operation of its output stage.
 35. A welder asdefined in claim 18 wherein each of said power sources includes a highspeed switching output stage for creating one of said currents withselected output waveform generated by a waveform generator controlling apulse width modulator circuit to determine the current operation of itsoutput stage.
 36. A welder as defined in claim 35 wherein said powersources are connected in series.
 37. A welder as defined in claim 34wherein said power sources are connected in series.
 38. A welder asdefined in claim 19 wherein said power sources are connected in series.39. A welder as defined in claim 18 wherein said power sources areconnected in series.
 40. A welder as defined in claim 35 wherein saidpower sources are connected in parallel.
 41. A welder as defined inclaim 34 wherein said power sources are connected in parallel.
 42. Awelder as defined in claim 19 wherein said power sources are connectedin parallel.
 43. A welder as defined in claim 18 wherein said powersources are connected in parallel.
 44. A welder as defined in claim 35including a wire feed speed controller associated with each powersource, and a voltage circuit to detect a given voltage associated withone of said electrodes and a controller with a circuit for adjustingsaid speed control input based upon said sensed voltage.
 45. A welder asdefined in claim 34 including a wire feed speed controller associatedwith each power source, and a voltage circuit to detect a given voltageassociated with one of said electrodes and a controller with a circuitfor adjusting said speed control input based upon said sensed voltage.46. A welder as defined in claim 19 including a wire feed speedcontroller associated with each power source, and a voltage circuit todetect a given voltage associated with one of said electrodes and acontroller with a circuit for adjusting said speed control input basedupon said sensed voltage.
 47. A welder as defined in claim 18 includinga wire feed speed controller associated with each power source, and avoltage circuit to detect a given voltage associated with one of saidelectrodes and a controller with a circuit for adjusting said speedcontrol input based upon said sensed voltage.
 48. A welder as defined inclaim 35 wherein said waveforms are AC waveforms in phase with eachother.
 49. A welder as defined in claim 19 including a short detector todetect a short between said trailing electrode and said workpiece and acircuit to clear said short by controlling the current of said secondpower source.
 50. A welder as defined in claim 19 including a firstsensing circuit to sense a first voltage associated with said first wirefeeder and a circuit to adjust said first speed based upon said firstvoltage.
 51. A welder as defined in claim 50 including a second sensingcircuit to sense a second voltage associated with said second wirefeeder and a circuit to adjust said second speed based upon said secondvoltage.
 52. A welder as defined in claim 18 including a first sensingcircuit to sense a first voltage associated with said first wire feederand a circuit to adjust said first speed based upon said first voltage.53. A welder as defined in claim 52 including a second sensing circuitto sense a second voltage associated with said second wire feeder and acircuit to adjust said second speed based upon said second voltage.